Process for the preparation of vitamin E

ABSTRACT

The invention concerns a novel method for preparing vitamin E. More particularly, it concerns a novel method for the condensation of Arimethylhydroquinone and isophytol.

[0001] The present invention relates to a novel process for thepreparation of vitamin E. It relates more particularly to a novelprocess for the condensation of trimethylhydroquinone and isophytol.

[0002] It is known, for example according to Japanese Patents No.60064977, No. 53144574 and No. 53015381, to condense isophytol withtrimethylhydroquinone in the presence of a Lewis acid, restricted tozinc chloride, in the presence of an inorganic acid chosen fromhalogenated acids and polyphosphoric acid in a solvent composed ofmethylene chloride and acetic acid.

[0003] It is also known, from Japanese Patents No. 59190987 and No.48072168, to condense trimethylhydroquinone with isophytol in thepresence of a catalyst based on zinc chloride and of an acid chosen fromhydrochloric acid or trichloroacetic acid; the reaction being carriedout in a solvent composed of an acetyl ester and in particular ofisopropyl acetate.

[0004] Finally, it is known, from Japanese patent No. 48072167, tocondense isophytol with trimethylhydroquinone under the same conditionsas above but removing the water of the reaction as it is formed duringthe condensation. Japanese Patent No. 6226976, which carries out thereduction of trimethylhydroquinone and the condensation with isophytolin the same solvent as above, that is to say isopropyl acetate,eliminates the presence of water between the two stages so as to avoidthe presence of water during the final condensation oftrimethylhydroquinone with isophytol.

[0005] The present reaction can be represented schematically in thefollowing way:

[0006] in which scheme A represents a halogen atom, a hydroxyl group oran acetoxy group.

[0007] It has transpired, entirely surprisingly, that, if it is desiredto restrict the consumption of TMHQ to 1 molar eq. with respect toisophytol, the presence of water in the condensation stage has afavourable effect on the reaction, contrary to that suggested by all ofthis prior art. The water prevents side reactions of TMHQ at thebeginning of the running in of isophytol.

[0008] Furthermore, it is known, according to Patent EP 0 850 937, thatit is possible to condense TMHQ with isophytol in the presence of waterprovided that a nonpolar solvent, such as an alkane, is used. Themaximum amount of water which can be used without harming the reactionyield and without distilling off the water formed during the reaction islimited to 1.5 mol of water per mole of isophytol. Under theseconditions, the influence of the amount of zinc chloride used was notstudied.

[0009] It has transpired that, when the process described previously iscarried out, that is to say when the catalysis with zinc chloride wascarried out in the absence of water and in a polar solvent, such asesters, there was a significant loss of TMHQ by transesterification withthe solvent. The present invention has made it possible to overcome thisproblem and has made it possible to carry out the condensation of TMHQwith isophytol in a polar solvent of the ester type and in the presenceof water.

[0010] The present invention thus consists in carrying out thecondensation of a phytol with trimethylhydroquinone in a polar solventof the ester type and in the presence of a Bronsted acid and of a zinchalide, characterized in that the reaction is carried out in thepresence of an amount of water of between 0.7 molar eq. and 2 molar eq.with respect to the number of moles of zinc halide and in the presenceof an amount of zinc halide of greater than 0.3 molar equivalent withrespect to the phytol.

[0011] The presence of this amount of water has numerous advantages;

[0012] it makes it possible to increase the reaction yield byapproximately 4%,

[0013] it makes it possible to recycle the zinc halide,

[0014] at equivalent stoichiometry for TMHQ and phytol, the presence ofwater increases the yield,

[0015] it prevents the esterification of TMHQ by the solvent.

[0016] Furthermore, in the case of solvents from the family of theesters, in contrast with the case of the hydrocarbons disclosed inPatent EP 0 850 937, the presence of water requires the use of amountsof zinc halides of greater than 0.3 molar equivalent with respect tophytol, so as:

[0017] to retain a yield>92%

[0018] to accelerate the kinetics of the reaction.

[0019] The phytol is chosen from isophytol or a phytyl halide, such asphytyl bromide, phytyl chloride or phytyl acetate.

[0020] The reaction is carried out in particular in the presence of aBronsted acid chosen from hydrochloric acid or sulphuric acid. It ispreferable to use hydrochloric acid.

[0021] The reaction is carried out in the presence of a polar solventwhich makes it possible to dissolve trimethylhydroquinone and the phytolused. Mention may be made, among polar solvents which may be used, ofesters and among these of ethyl, propyl, isopropyl, butyl or isobutylacetate; acetates having a longer chain are not preferred although theycan be used; the viscosity of the solvent simply increases with thelength of the chain, which is not very favourable to the reaction.Esters of longer organic acids than the acetates can also be used, inparticular esters of propionic, butyric or isobutyric, valeric orisovaleric acid, but, as in the case of the acetates, the increase inthe length of the chain increases the viscosity of the medium, which isnot always favourable to the reaction. It is preferable, among all theseesters, to use isopropyl acetate.

[0022] The presence of water in the reaction medium, which improves thecondensation yield, leads in some cases to the presence of a two-phasesystem. In this case, it is advantageous to add an organic acid chosenfrom acetic acid, propionic acid or butyric acid in order to prevent thephases from separating. It is preferable to use the acid correspondingto the ester used as solvent. Thus, when an acetate is used, it ispreferable to add acetic acid.

[0023] The amount of organic acid added corresponds to approximately 3to 20 times the amount by weight of water present in the medium.

[0024] The catalyst used to promote the condensation is chosen from zinchalides. It is preferable to use zinc chloride. It is advantageous alsoto use a Bronsted acid chosen from hydrochloric acid or sulphuric acid.

[0025] According to a better way of implementing the invention, thecatalyst is used according to a ratio of approximately 0.7 to 1.2equivalents per mole of phytol.

[0026] The advantage of using this amount of Lewis acid with respect tothe prior art, which uses less thereof, is:

[0027] to increase the reaction rate,

[0028] to improve the selectivity of the condensation.

[0029] The molar ratio of the hydroquinone to the phytol is preferablybetween 1 and 1.5 and it is highly preferably between 1 and 1.2. TheBronsted acid is preferably used according to a molar amount of between4% and 16% with respect to the number of moles of phytol.

[0030] For a better implementation of the invention, it is preferable tooperate at a temperature of between 55° C. and 75° C.

[0031] The α-tocopherol obtained is separated from the reaction mediumby liquid/liquid extraction.

[0032] The following stage of the process for the preparation of vitaminE, when it is provided in the acetate form, consists in carrying out theacetylation of the α-tocopherol.

[0033] This stage is carried out according to a novel method whichconsists in acetylating the α-tocopherol with acetic anhydride in theabsence of any solvent, that is to say neat.

[0034] The acetylation is carried out in the presence of a catalystcomposed of an inorganic acid chosen from sulphuric acid or phosphoricacid or of an alkaline acetate.

[0035] It has been discovered that it is preferable to employ phosphoricacid or sodium acetate as it is possible, with these catalysts, tocompletely avoid colouring the reaction medium during the acetylation.The tocopheryl acetate obtained is even lighter than the startingtocopherol. It is preferable to use a molar ratio of the aceticanhydride to the tocopherol of between 1 and 1.8. Use if preferably madeof 0.7 to 2 molar % of acid as acetylation catalyst when the latter issulphuric acid, 1 to 2 molar % when the acetylation catalyst isphosphoric acid and 5 to 10 molars when the acetylation catalyst issodium acetate.

[0036] The present invention also relates to a complete process for thepreparation of vitamin E from trimethylbenzoquinone, the entire processbeing carried out in the same solvent, which is a good solvent fortrimethylbenzoquinone, for trimethylhydroquinone and for the phytol.This solvent is in particular a polar solvent, preferably an ester andhighly preferably isopropyl acetate.

[0037] It consists, in a first stage, in carrying out a hydrogenation oftrimethylbenzoquinone with a hydrogenation catalyst, preferably asupported catalyst, chosen from palladium and platinum. It is preferableto use palladium supported on charcoal.

[0038] The second stage consists, after filtration so as to remove thecatalyst, in carrying out the condensation of the trimethylhydroquinoneobtained in the first stage with the phytol under the conditionsdescribed above and in particular in the presence of a zinc halide, of aBronsted acid and of water and very particularly in the presence of zincchloride, of hydrochloric acid and of water. At the end of the reaction,the catalyst is extracted with water and this aqueous phase isconcentrated, in particular from 80 wt % to 91 wt % of ZnCl₂, so as toleave at most, including the water from the Bronsted acid, only twomoles of water per mole of zinc halide recycled to the second stage ofthe process.

[0039] The organic phase is then preferably concentrated to dryness, soas to remove the reaction solvent and its possible by-products, and thenacetylated neat as described above.

[0040] The process for the extraction of vitamin E acetate issubsequently carried out conventionally and in a way known to a personskilled in the art. The medium is extracted with a solvent which isimmiscible or virtually immiscible with water, then washed with an acidsolution, so as to hydrolyze the remaining acetic anhydride, and thenwashed in alkaline medium, to deacetylate the TMHQ acetates. The aqueousphase comprising the alkaline salt of TMHQ is isolated by a two-phaseseparation, this phase is acidified and the TMHQ is extracted with thereaction solvent, that is to say the ester, which allows it to berecycled to the condensation stage.

[0041] The invention will be more fully described with the help of thefollowing examples, which should not be regarded as limiting theinvention.

EXAMPLES Preparation of TMHQ in Solution by Hydrogenation Example 1

[0042]3.1 g of Pd/c (3%, 52% H₂O) and 3 550 g of IPAC are charged to an8 1 hydrogenation reactor rendered inert beforehand with nitrogen. Thereactor is placed under 0.5 bar of hydrogen with stirring. The medium isheated to 80° C. and is maintained at this temperature for 10 minutes.

[0043] The reactor is subsequently pressurized to 2 bar of hydrogen.Hydrogenation is carried out semi-continuously by simultaneous additionof 96.5% w/w TMBQ (total charge=700.3 g) and of hydrogen, so as toremain at 80° C. and under 2 bar of hydrogen. The end of the reaction isdetected by the fall in the hydrogen flow rate.

[0044] The reaction medium is degassed and then purged with nitrogen.The reaction medium is filtered while hot under nitrogen pressure. Thesolution of 708.2 g of TMHQ in IPAC is obtained which is ready for usein the condensation reaction. The hydrogenation yield is 99.8%.

TMHQ/IsoPhytol Condensation Reactions in the Absence of Water Example 2

[0045] A hot solution of 76 g of TMHQ in IPAC comprising 16% w/w of IPACis charged with stirring to a 1 l reactor. This solution is concentratedwith stirring to 38% w/w by distillation of IPAC at 45° C. under vacuum.50.1 g of 98% w/w ZnCl₂, dissolved in 72 g of acetic acid under warmconditions, are added to the suspension obtained, followed by 4 g of 92%w/w of sulphuric acid. The reaction medium is heated to 75° C. 162 g of91.5% w/w isophytol are then run in over 43 min. After the isophytol hasfinished being run in, the reaction is maintained at 75° C. for 60 min.100 g of water are charged with stirring and the mixture is subsequentlyseparated by settling. The volatile products are removed from theorganic phase by distillation at 75° C. under vacuum. 1 g of 92% w/wsulphuric acid is charged at 75° C. and then 88.5 g of 98% w/w aceticanhydride are run in at this temperature over 10 min. The reactionmedium is heated to 105° C. over 20 min and then rapidly cooled to 35°C. 1 200 g of hexane are charged with stirring, followed by 71 g ofwater. The two phases are separated by settling. The organic phase isagain washed with 71 g of water. The organic phase is evaporated on arotary evaporator at 60° C. under vacuum for 2 h.

[0046] 254.8 g of crude 84.2% w/w tocopheryl acetate (Toco) are obtained(yield=90.9%).

[0047] The procedure of Example 3 is identical to that of Example 2.Only the running-in time changes (84 min). The parameters are shown inTable 1. TABLE 1 Influence of the absence of water. Mainte- Total Toconance H₂O** Toco Yd (% Exam- time AcOH ZnCl₂ Acid T H₂O (mol/mol assaypure/ ple (min) (g) (eq)* (eq) (° C.) (g) ZnCl₂) (%) pure) 2 60 72 0.72H₂SO₄ 75 0 0.05 84.2 90.9 (0.08) 3 60 72 0.72 H₂SO₄ 75 0 0.05 81.9 87.2(0.08)

TMHQ/Isophytol Condensation Reactions in the Presence of Water Reactionswith Acid=36% HCl Without Addition of Additional Water Example 4

[0048] A hot solution of 76 g of TMHQ in IPAC comprising 16% w/w of IPACis charged with stirring to a 1 l reactor. This solution is concentratedwith stirring to 38% w/w by distillation of IPAC at 45° C. under vacuum.50.1 g of 98% w/w ZnCl₂, dissolved in 72 g of acetic acid under hotconditions, are added to the suspension obtained, followed by 8.1 g of36% w/w hydrochloric acid. The reaction medium is heated to 75° C. 161.6g of 91.6% w/w isophytol are then run in over 47 min. After theisophytol has finished being run in, the reaction is maintained at 75°C. for 60 min. 100 g of water are charged with stirring and the mixtureis subsequently separated by settling. The volatile products are removedfrom the organic phase by distillation at 75° C. under vacuum. 1.1 g of92% w/w sulphuric acid are charged at 75° C. and then 88.6 g of 98% w/wacetic anhydride are run in at this temperature over 10 min. Thereaction mixture is heated to 105° C. over 30 min and then rapidlycooled to 35° C. 120 g of hexane are charged with stirring, followed by70 g of water. The two phases are separated by settling. The organicphase is again washed with 70 g of water. The organic phase isevaporated on a rotor evaporator at 60° C. under vacuum for 2 h.

[0049] 258 g of crude 86.4% w/w tocopheryl acetate (Toco) are obtained(yield=94.3%).

[0050] The procedures of Examples 5 and 6 are identical to that ofExample 4. The parameters modified in the examples are specified inTable 2. TABLE 2 Influence of the presence of water. Total Mainte- H₂O**Toco nance H₂O (mol/ Toco Yd (% Exam- time AcOH ZnCl₂ Acid T added molassay pure/ ple (min) (g) (eq)* (eq) (° C.) (g) ZnCl₂) (%) pure) 4 60 720.72 36% 75 0 0.75 86.4 94.3 HCl (0.16) 5 60 72 0.72 36% 75 0 0.75 87.893.4 HCl (0.16) 6 90 47 0.45 36% 62 0 0.75 89.5 97 HCl (0.09)

TMHQ/Isophytol Condensation Reactions in the Presence of Water Reactionswith Acid=36% HCl or 92% H₂SO₄ with Addition of Water Influence of theWater Content and of the ZnCl₂ Stoichiometry Example 7

[0051] A hot solution of 76 g of TMHQ in IPAC comprising 16% w/w of IPACis charged with stirring to a 1 l reactor. This solution is concentratedwith stirring to 38% w/w by distillation of IPAC at 45° C. under vacuum.50.1 g of 98% w/w ZnCl₂, dissolved in 72 g of acetic acid under warmconditions, 4.28 g of 92% w/w sulphuric acid and 5 g of water are addedto the suspension obtained. The reaction mixture is heated to 75° C. 162g of 91.5% w/w isophytol are then run in over 40 min. After theisophytol has finished being run in, the reaction is maintained at 75°C. for 60 min. 200 g of water are charged with stirring and the mixtureis subsequently separated by settling. The volatile products are removedfrom the organic phase by distillation at 75° C. under vacuum. 1.1 g of92% w/w sulphuric acid are charged at 75° C. and then 88.5 g of 98% w/wacetic anhydride are run in at this temperature over 10 min. Thereaction medium is heated to 105° C. over 30 min and is then rapidlycooled to 35° C. 200 g of hexane are charged with stirring, followed by50 g of water. The two phases are separated by settling. The organicphase is again washed with 30 g of water. The organic phase isevaporated on a rotary evaporator at 60° C. under vacuum for 2 h.

[0052] 253.2 g of crude 88.2% w/w tocopheryl acetate (Toco) are obtained(yield=94.6%).

[0053] The procedures of Examples 8 to 15 are identical to that ofexample 7. The sulphuric acid is sometimes replaced by hydrochloricacid. The parameters modified in the examples are specified in Table 3.TABLE 3 Influence of the water content and of the ZnCl₂ stoichiometry.Toco Mainte- H₂O** Yd nance (mol/ Toco (% Exam- time AcOH ZnCl₂ Acid TH₂O mol assay pure/ ple (min) (g) (eq)* (eq) (° C.) (g) ZnCl₂) (%) pure)7 60 72 0.72 H₂SO₄ 75 5 0.75 88.2 94.6 (0.08) 8 60 0 0.72 H₂SO₄ 75 111.65 86.6 93.8 (0.04) 9 120 18 0.18 36% HCl 75 0 1.5 83.2 90.1 (0.08) 1040 36 0.36 H₂SO₄ 75 2.5 0.75 93.4*** 95.5 (0.04) 11 60 66 0.63 H₂SO₄ 624.3 0.75 89.6 98.4 (0.063) 12 60 47 0.45 H₂SO₄ 62 3.07 0.75 89.4 98.3(0.045) 13 80 40 0.72 36% HCl 62 2.8 1.12 90.6 97.5 (0.15) 14 80 0 0.4536% HCl 62 3.07 1.5 88.3 95.4 (0.09) 15 90 45 0.72 36% HCl 62 9.6 18.887.8 95.8 (0.09)

TMHQ/Isophytol Condensation Reactions in the Presence of Water Influenceof the TMHQ and ZnCl₂ Stoichiometry Example 16

[0054] A hot solution of 76 g of TMHQ in IPAC comprising 16% w/w of IPACis charged with stirring to a 1 l reactor. This solution is concentratedwith stirring to 38% w/w by distillation of the IPAC at 45° C. undervacuum. 49.8 9 of 98% w/w ZnCl₂, dissolved in 45 g of acetic acid underwarm conditions, 4.7 g of 36% w/w hydrochloric acid and then 4.8 g ofwater are added to the suspension obtained. The reaction mixture isheated to 72° C. 160.5 g of 92.2% w/w isophytol are then run in over 20min. After the isophytol has finished being run in, the reaction ismaintained at 72° C. for 40 min. 100 g of water are charged withstirring and the mixture is subsequently separated by settling. A secondwashing is carried out with 60 g of water. The volatile products areremoved from the organic phase by distillation at 75° C. under vacuum.0.6 g of 92% w/w sulphuric acid are charged at 85° C. and then 68 g of92% w/w acetic anhydride are run in at this temperature over 6 min. Thereaction medium is maintained at this temperature for 60 min and thenrapidly cooled to 35° C. 240 g of hexane are charged with stirring,followed by 220 g of water and by 9 g of 92% w/w H₂SO₄. The two phasesare separated by settling. The organic phase is then washed with amixture of 100 g of water and 12 g of 50% NaOH. The organic phase isevaporated on a rotor evaporator at 60° C. under vacuum for 2 h.

[0055] After evaporation of partial purification, 232.7 g of 94.8% w/wtocopheryl acetate (Toco) are obtained (yield=93.3%).

[0056] The residual TMHQ is recovered by acidification of the alkalineaqueous phase with 92% w/w H₂SO₄ and then extraction with IPAC. Thesolution of recovered TMHQ in IPAC can be recycled in the TMHQ/Isophytolcondensation.

[0057] The procedures of Examples 17 to 19 are identical to that ofExample 16. The parameters modified in the examples are specified inTable 4. TABLE 4 Influence of the water content and of theZnCl₂stoichiometry. Maintenance AcOH TMHQ ZnCl₂ Acid Total H₂O** Tocoassay Toco Yd (% Example time (min) (g) (eq) (eq)* (eq) T (° C.) H₂O (g)(mol/mol ZnCl₂) (%) pure/pure) 16 40 45 1.01 0.72 36% HCl 72 4.8 1.1294.7*** 93.3 (0.09) 17 40 45 1.05 0.72 36% HCl 75 4.8 1.12 95*** 95.7(0.09) 18 20 45 1.15 0.72 36% HCl 75 4.8 1.12 93.2*** 96.2 (0.09) 19 4062 1.15 1 36% HCl 75 7.6 1.12 96.4*** 98 (0.09)

TMHQ/Isophytol Condensation Reactions in the Presence of Water Recyclingof ZnCl₂ Example 20

[0058] A hot solution of 76 g of TMHQ in IPAC comprising 16% w/w of IPACis charged with stirring to a 1 l reactor. This solution is concentratedwith stirring to 38% w/w by distillation of the IPAC at 45° C. undervacuum. 49.8 g of 98% w/w ZnCl₂, 45 g of acetic acid, 4.6 g of 36% w/whydrochloric acid and then 4.8 g of water are added to the suspensionobtained. The reaction medium is heated to 62° C. 161.6 g of 91.6% w/wisophytol are then run in over 60 min. After the isophytol has finishingbeing run in, the reaction is maintained at 62° C. for 50 min. 100 g ofwater are charged with stirring and the mixture is subsequentlyseparated by settling. A second washing is carried out with 60 g ofwater. In all, 269.7 g of aqueous phase comprising more than 99.5% ofthe ZnCl₂ charged are recovered. The volatile products are removed fromthe organic phase by distillation at 75° C. under vacuum. 0.7 g of 92%w/w sulphuric acid are charged at 70° C. and then 68 g of 92% w/w aceticanhydride are run in at this temperature over 10 min. The reactionmedium is maintained at this temperature for 90 min and then rapidlycooled to 35° C. 240 g of hexane are charged with stirring, followed by220 g of water and by 9 g of 92% w/w H₂SO₄. The two phases are separatedby settling. The organic phase is then washed with a mixture of 100 g ofwater and 12 g of 50% NaOH. The organic phase is evaporated on a rotaryevaporator at 60° C. under vacuum for 2 h.

[0059] After evaporation and partial purification, 237.8 g of 96% w/wtocopheryl acetate (Toco) are obtained (yield=97%).

[0060] The aqueous phase (269.7 g), comprising ZnCl₂ and HCl, isevaporated on a rotary evaporator under a vacuum of 5 to 10 torr atapproximately 115° C. until a suspension is obtained (˜90% w/w ofZnCl₂). 45.6 g of AcOH are added to this suspension in order to obtain asolution. The exact ZnCl₂ assay is quantitatively determined bycolorimetry. This ZnCl₂ solution is used in the following TMHQ/Isophytolcondensation reaction, where the additional water charge is no longernecessary. The amounts of reactants (TMHQ, 36% HCl and isophytol) arecalculated on the basis of the amount of ZnCl₂ recycled, so as tomaintain a ZnCl₂/Isophytol molar ratio of 0.72 eq.

[0061] The procedures of Examples 21 to 23 are identical to that ofExample 20. TABLE 5 Recycling of ZnCl₂. Maintenance AcOH TMHQ ZnCl₂ AcidTotal H₂O** Toco assay Toco Yd (% Example Recycling time (min) (g) (eq)(eq)* (eq) T (° C.) (mol/mol ZnCl₂) (%) pure/pure) 20 0 50 45 1.01 0.7336% HCl 62 1.16 96*** 97 (0.09) 21 1 50 45.6 1.01 0.73 36% HCl 62 1.1495.6*** 97.2 (0.09) 22 2 50 43.6 1.01 0.70 36% HCl 62 1.25 95.3*** 97.2(0.09) 23 3 50 42.75 1.01 0.68 36% HCl 62 1.34 95.8*** 97.2 (0.09)

[0062] Acetylation catalysts: Influence on the coloration of thetocopheryl acetate (Toco)

Examples 24 to 26

[0063] The procedure and the charges of the TMHQ/Isophytol condensationare identical to those in Example 16.

[0064] Only the acetylation stage is changed. The parameters are shownin Table 6. TABLE 6 Influence of the acetylation catalyst on the Tococoloration Time Toco Cata. for Mainte- Yd Ex- eq. running nance Toco (%am- Cata- (mol Ac₂O T in Ac₂O time assay pure/ ple lyst %) (eq) (° C.)(min) (min) (%) pure) 24 92% 2 1.3 70 7 90 89.9 97.5 H₂SO₄ 25 85% 2 1.395 7 90 89.14 96.6 H₂PO₄ 26 AcONa 10 1.3 110 7 90 89.43 98.6

[0065] The Toco colorations in solution were measured by the Gardnermethod.

[0066] The Toco samples were diluted in cyclohexane. The solution isintroduced into a 10 mm quartz cell. The analysis is carried out in the400-700 nm spectral range.

[0067] The trichromatic coordinates are as follows: Catalyst x y Y H₂SO₄0.5452 0.4325 0.84 H₃PO₄ 0.4553 0.4596 40.67 AcONa 0.4424 0.4594 67.71

[0068] The representation of these points on the corresponding Gardnercurve is as follows:

[0069] The curve shows that H₃PO₄ and AcONa result in products which areless coloured than H₂SO₄.

1. Process for the condensation of a phytol with trimethylhydroquinonein a polar solvent of the ester type and in the presence of a Bronstedacid and of a zinc halide, characterized in that the reaction is carriedout in the presence of an amount of water of between 0.7 molar eq. and 2molar eq. with respect to the number of moles of zinc halide used and inthe presence of an amount of zinc halide of greater than 0.3 molarequivalent with respect to the phytol.
 2. Process according to claim 1characterized in that the amount of zinc halide is between 0.7 and 1.2molar eq. with respect to the phytol.
 3. Process according to claim 1,characterized in that the zinc halide is zinc chloride.
 4. Processaccording to claim 1, characterized in that the solvent is chosen fromalkyl acetates comprising 2 to 4 carbon atoms in the alkyl chain. 5.Process according to claim 1, characterized in that the Bronsted acid ischosen from hydrochloric acid or sulphuric acid.
 6. Process according toclaim 5, characterized in that the molar amount of Bronsted acid isbetween 4% and 16% with respect to the number of moles of phytol. 7.Process according to any one of the preceding claims, characterized inthat an organic acid, and preferably acetic acid, is added to thereaction medium.
 8. Process according to claim 7, characterized in thatthe amount by weight of organic acid used is between 3 and 20 times theamount by weight of water present in the medium.
 9. Process for thepreparation of α-tocopherol acetate, characterized in that theα-tocopherol is brought into contact with acetic anhydride in thepresence of an inorganic acid chosen from sulphuric acid or phosphoricacid or in the presence of an alkaline acetate and in the absence of anysolvent.
 10. Process according to claim 9, characterized in that use ismade of 0.7 to 2 molar % of acid as acetylation catalyst when the latteris sulphuric acid, 1 to 2 molar % when the acetylation catalyst isphosphoric acid and 5 to 10 molar % when the acetylation catalyst issodium acetate.
 11. Process for the preparation of α-tocopherol acetate,characterized in that, in a first stage, a hydrogenation oftrimethylbenzoquinone in a solvent described in claim 4 is carried outwith a supported hydrogenation catalyst chosen from palladium andplatinum, in a second stage, after filtration, the condensation of thetrimethylhydroquinone obtained in the first stage with the phytol iscarried out under the conditions described in claim 1, in a third stage,the catalyst is extracted with water, the aqueous solution obtained isconcentrated under warm conditions so as to leave remaining only at mosttwo moles of water per mole of Lewis catalyst and is recycled to thesecond stage of the process, in a fourth stage, the organic phase isconcentrated to dryness, so as to remove the reaction solvent and itspossible by products, and then acetylated neat under warm conditionsdescribed in claim 9, the medium is extracted with a solvent which isimmiscible or virtually immiscible with water, then washed with an acid,so as to hydrolyse the remaining acetic anhydride, and then washed inalkaline medium, to deacetylate the TMHQ acetates, in a fifth stage, atwo-phase separation is carried out which makes it possible to isolatethe aqueous phase comprising the alkaline salt of TMHQ, which isacidified in the presence of the reaction solvent and is recycled to thesecond stage.